docs: def export_public_key(user_id, env=None, sp=subprocess):
      """Export GPG public key for specified `user_id`."""
      args = gpg_command(['--export', user_id])
      result = check_output(args=args, env=env, sp=sp)
      if not result:
          log.error('could not find public key %r in local GPG keyring', user_id)
          raise KeyError(user_id)
      return result